An aneurysm is an unfavorable condition resulting from arterial sclerosis, inflammation and other causes that will grow larger and lead to fatal ruptures when left unattended. Since current medicinal treatments hardly produce any good results, excision and replacement of dilatations have conventionally been resorted to. However, this condition appears frequently in aged persons and is often associated with the disturbances of many organs (such as the brain, heart and liver). Therefore, applicability of surgical operations, which can often cause exorbitant stresses, is limited. Thus, intravascular treatments using catheters whose operative stresses are relatively moderate have been receiving the attention of the world. The use of stents is one of such treatments in popular use.
The stent is a term to generally denote artificial tubular structures that are inserted into blood vessels and other tubular organs in the body to support them. When, for example, stricture or other defamation has occurred in blood vessels, gallbladers, gullets, bowels, ureters and other internal tubular organs, a stent is inserted into them to prevent the recurrence of such stricture or deformation by supporting them. Generally, the main body of the stent is elastic, being made of metal wires or other similar materials. The main body of the stent is designed so that it can radially expand and constrict repeatedly. The stent is often inserted in the body using a catheter. Therefore, the stent must become smaller than the inside diameter of the catheter when it constricts so that it can be contained within the catheter. When released from inside the catheter, the stent must radially expand to the desired diameter.
Several types of self-expanding stents having elastic tubular shapes are made of wires of stainless steel, shape memory alloy or other metals and are intended for use in blood vessels for the treatment of aneurysm, as disclosed, for example, in Japanese Provisional Patent Publications Nos. 24072 and 47134 of 1995 and Japanese Provisional Patent Publications Nos. 500272 of 1995 and 299456, 502428 and 511437 of 1996. These self-expanding stents are mainly used as stent grafts (the term graft denotes an artificial blood vessel inserted into a human blood vessel) that are sutured and fixed in laminar polyester blood vessels. A stent graft compressed and loaded in a thin catheter is pressed into an aneurysm from a part of a peripheral artery (mainly the femoral artery by way of the catheter). The stent graft is then allowed to expand on its own and dwell in the aneurysm to achieve both occlusion of the dilatation and repair of vascular flow. The intravascular treatment using stent grafts causes only mild operative stresses, thus lightening burdens of stresses imposed on patients and being applicable to wider varieties of aneurysms than conventional methods. This treatment is now very effective for cases of aneurysms.
To securely close an aneurysm by the use of an indwelling stent graft, it is necessary to keep the stent tightly fitted in the artery by ensuring that the stent covers not only the aneurysm itself but also the normal arteries at its center and on its peripheries. However, this can sometimes block up main arteries branching from the aneurysm and nearby sound aortas, which can lead to other organ derangements. The renal, inferior mesenteric and hypogastric arteries are the main visceral arteries affected by the dominal aneurysm. Occlusion of these arteries can lead to renal and intestinal ischemic dysfunctions. With aneurysms of the thoracic aorta, occlusion of the intercostal artery can cause disturbance of the spinal cord blood flow which, in turn, can result in a serious complication called paraplegia (lower-body motor paralysis).
However, the intravascular stents proposed so far cannot be re-constricted and recovered after they have been once released from catheters and allowed to expand on their own. As such, they present a serious problem in that they cannot be recovered from within the blood vessel even after an organ or blood flow derangement has occurred. In addition, if they have been placed in the wrong place, they are difficult to move to the right place for correction. Thus, their applicability is limited by safety considerations.
The object of this invention is to provide a stent that can be re-constricted and recovered after it has been released from a catheter and allowed to expand on its own.